Power semiconductor devices typically include a low-doped drift zone across which the blocking voltage drops. When the drift zone is formed in an epitaxial layer grown on a heavily doped semiconductor base, in-situ doping during the epitaxial growth facilitates a highly homogeneous distribution of the dopants within the epitaxial layer. Since the growth rate of epitaxial layers is about 1 μm per minute, the process is comparatively expensive for drift zones with a thickness of 100 μm and more. Therefore, semiconductor wafers for the manufacture of semiconductor devices with high blocking capability are typically obtained by sawing from silicon ingots, which grow from a localized floating melting zone of a rod from a raw material. During the floating zone melting process, the growing silicon crystal typically incorporates dopant atoms at comparatively high homogeneity across the length and the diameter of the silicon ingot but the costs of this process are relatively high and the maximum available wafer diameter is 12″. Drawing a silicon ingot from molten raw material in a crucible in a Czochralski process, on the other hand, provides silicon ingots with diameters greater than 12″ in an economic way but at the costs of comparatively high axial inhomogeneity.
It is desirable to improve the manufacture of power semiconductor devices.